The present invention is directed to a positive electrode active material for a magnesium electrochemical cell and a magnesium secondary battery with a cathode based on the active material.
Lithium ion batteries have been in commercial use since 1991 and have been conventionally used as power sources for portable electronic devices. The technology associated with the construction and composition of the lithium ion battery (LIB) has been the subject of investigation and improvement and has matured to an extent where a state of art LIB battery is reported to have up to 700 Wh/L of energy density. However, even the most advanced LIB technology is not considered to be viable as a power source capable to meet the demands for a commercial electric vehicle (EV) in the future. For example, for a 300 mile range EV to have a power train equivalent to current conventional internal combustion engine vehicles, an EV battery pack having an energy density of approximately 2000 Wh/L is required. As this energy density is close to the theoretical limit of a lithium ion active material, technologies which can offer battery systems of higher energy density are under investigation.
Magnesium as a multivalent ion is an attractive alternate electrode material to lithium, which can potentially provide very high volumetric energy density. It has a highly negative standard potential of −2.375V vs. RHE, a low equivalent weight of 12.15 g/eq and a high melting point of 649° C. Compared to lithium, it is easy to handle, machine and dispose. Because of its greater relative abundance, it is lower in cost as a raw material than lithium and magnesium compounds are generally of lower toxicity than lithium compounds. All of these properties coupled with magnesium's reduced sensitivity to air and moisture compared to lithium, combine to make magnesium an attractive alternative to lithium as an anode material.
Production of a battery having an anode based on magnesium, requires a cathode which can reversibly adsorb and desorb magnesium ions and an electrolyte system which will efficiently transport magnesium ions. Significant effort in each of these areas is ongoing in many research organizations throughout the world and active materials under investigation include sulfur in various forms, including elemental sulfur, materials known as Chevrel compounds of formula MgxMo6Tn, (wherein x is a number from 0 to 4, T is sulfur, selenium or tellurium, and n is 8) and various metal oxides such as MnO2 (alpha manganese dioxide stabilized by potassium), V2O5 and ion stabilized oxides or hollandiates of manganese, titanium or vanadium.
Carbon based materials have been extensively investigated as electrode materials in Li-ion batteries. Such materials offer the advantage of being abundant and environmentally friendly. However, the application of carbon as an active magnesium intercalation material in rechargeable magnesium batteries has not been reported. General carbon phases, such as graphite and hard carbon, are electrochemically inert with respect to magnesium. The inventors believe these materials cannot efficiently delocalize the charges from divalent Mg2+. Chevrel phase materials which are the only reported magnesium intercalation materials are believed to function because the Mo6 atomic cluster in the crystal structure can attain the electroneutrality from the intercalation of Mg2+. However, batteries having cathodes based on chevrel materials reported to date have low capacity and low working potential.
The inventors have therefore investigated carbon materials which are arranged in atomic clusters as possible intercalation materials. Utility of such materials as magnesium intercalants for cathodes in a magnesium battery has not been reported to date.
Pontiroli et al. (CARBON 51 (2013) 143-147) describe formation of a two dimensional fullerene polymeric network with Mg intercalated according to the formula: Mg2C60. Conductivity of the system is described as showing that Mg ions diffuse through the fullerene lattice.
Even et al. (Int. J. Mol. Sci., 2004, 5,333-346) describes performance of mathematical modelling calculations of electron energy levels based on Mg+ ion in a fullerene model identified as a “jellium-shell.”
Heguri et al. (Chemical Physical Letters, 490 (2010) 34-37) describes preparation and characterization of C60 films containing varying controlled amount of diffused Mg. The films are semiconducting or insulating and not superconducting as in the case of Ca5C60, Sr4C60, and Ba4C60.
Borondics et al. (Solid State Communications, 127 (2003) 311-313) describes the solid state synthesis of Mg4C60 and characterization of the product by X-ray powder diffraction and Raman spectroscopy.
Jin et al. (U.S. Pat. No. 7,994,422) describes a particulate structure, comprising: a metal oxide semiconductor particle comprising a pore; a catalytic metal particle arranged within the pore of the porous metal oxide semiconductor particle, a size of the catalytic metal particle being 5 nm to 100 nm; and a carbon nanotube arranged within the pore of the metal oxide semiconductor particle, wherein the carbon nanotube is grown based on the catalytic metal particle arranged within the pore of the porous metal oxide semiconductor particle.
Matsubara et al. (U.S. Pat. No. 6,869,730) describes a binder system for a positive electrode of a lithium secondary battery. Fullerene is included in a list of possible active materials which can absorb and desorb lithium ions.
Uetani (US 2011/0005598) describes an organic photoelectric conversion element that has an anode and a cathode, an active layer arranged between the anode and the cathode and containing an electron accepting compound and an electron donating compound, and a functional layer arranged between the anode and the active layer so as to be adjacent to the anode, wherein the electron accepting compound is a fullerene derivative.
Lee et al. (US 2011/0091775) describes a lithium secondary battery having a negative electrode obtained by coating an aqueous mixture, including negative electrode active materials, a water-dispersible binder, and a conduction agent, on a current collector and then drying to remove the water. The negative electrode active materials can include carbon and graphite materials, such as natural graphite, artificial graphite, expanded graphite, carbon fiber, non-graphitizing carbon, carbon black, carbon nanotubes, fullerenes, and activated carbon; metal, such as Al, Si, Sn, Ag, Bi, Mg, Zn, In, Ge, Pb, Pd, Pt, or Ti which can be alloyed with lithium, and a compound containing the elements; a complex of metal and a compound thereof and carbon and graphite materials; and nitrides containing lithium.
Gennett et al. (US 2012/0295166) describes an organic radical battery (ORB) which is defined as a hybrid solid-state electrochemical device such as an energy storage/discharge device (e.g., a lithium-ion battery or the like) or an electrochromic device (e.g., smart window). The device may include an anode composed of a pre-lithiated nanostructured material, a cathode composed of a stable polymeric organic radical-based material, an electrolyte composed of a high performance solidstate polymer; and optional anode and cathode current collectors. Lithium and magnesium based anodes are described. The magnesium anodes include magnesium-doped carbon that may be further doped with boron. The anode may exist in a nanostructured form such as a nanostructured inorganic radical based on nanostructured carbon. The anode may be made of a heterogeneous carbon-based anode material and may be doped or undoped nanotubes (e.g., single walled nanotubes (SWNTs), double-wall nanotubes, multi-wall nanotubes, fullerenes, microbeads such as mesocarbon microbeads. The anode may be composed of carbon nanotubes (such as single-wall, double-wall, and/or multi-wall nanotubes), carbon fibers, fullerenes, graphene, and/or any carbon based nanostructured material, including doped carbon nanostructures, e.g., boron or nitrogen-doped nanotubes and/or BCN nanostructures (e.g., any hybrid nanotubes constructed of boron (B), carbon (C), and/or nitrogen (N) elements or other nanostructures of the so-called BCN material system).
Zhuo et al. (CN101414678B) describes a cathode material for a lithium ion battery which is formed by ball milling a metal with a carbonaceous material and then reducing the metal with hydrogen to form the metal hydride. The carbonaceous material is indicated to be graphite.
Yoshiaki et al. (JP09045312) describes a nonaqueous lithium secondary battery having a negative electrode constructed of carbon nanotube based based on a fullerene derivative. At least one of Li, Na, K, Mg and Ca is contained in the electrode tube. A conventional cathode capable of storing and releasing lithium ions is employed.
Tori et al. (JP09283173) describes a battery composed of a negative electrode based on a fullerene compound and a reduced metal. A metal oxide is used as the positive electrode.
Yoshiaki et al. (JP3475652) describes an alkaline storage battery having a negative electrode based on a fulleride containing a metal and a nickel hydroxide containing both cobalt and zinc in the form of a hydroxide or oxide as the positive electrode.
The utility of carbon cluster materials such as fullerene as a magnesium intercalant material, cathodes constructed of such material and magnesium batteries containing such cathodes has not been disclosed in any of these references.
Therefore, an object of the present invention is to provide a cathode active material based on a carbon cluster composition which meets the requirements of a high energy magnesium battery and overcomes the deficiencies of the conventionally known intercalant materials.
Another object of the present invention is to provide a magnesium battery containing a cathode based on a carbon cluster composition which has significantly improved energy density and performance in comparison to known magnesium electrochemical devices.